Asphaltic substances are well known in the art. Generally pitchy or oleaginous materials, they include a wide variety of substances including bitumens, liquid and solid hydrocarbons, natural and synthetic resins, ester gums, stearines, and/or waxes together with fluxing oils which may be petroleum products, drying or nondrying oils or fatty acids, etc. Such materials generally have the common characteristic of being immiscible with water and becoming fusible with heat. Under proper conditions, asphaltic materials form aqueous emulsions with emulsifying agents. The emulsions comprise the asphaltic material in liquid or semi-solid form dispersed as minute, discrete globules or particles which do not coalesce but which, when mixed with mineral aggregate, will break and cause the asphalt to deposit on the aggregate. Subsequently, the asphaltic materials cure to form an agglomerated coalescent or coherent mass.
Asphalt emulsions are widely used in highway construction, surfacing and maintenance. They are also used in various other applications where water repellent surfaces are needed. Slow-setting emulsions are grades of emulsions that are sufficiently stable to allow mixing with fine or dusty aggregate mineral particles and further processing before setting to a coherent mass. Such grades of asphalt emulsions (SS-1 grade), when anionic, react chemically with portland cement constituents forming a water-insoluble salt and thus possess valuable water-resistant characteristics.
Asphalt emulsions generally contain stabilizers which retard the settling of finely divided particles. A typical method of producing the emulsions comprises the step of combining the asphalt with the emulsifier and subjecting the mixture to mechanical shearing action such as that generated in a colloid mill or homogenizer to form droplets of asphaltic material that are quickly covered by the emulsion-conditioner to provide a stable emulsion. Typical emulsifying agents include certain thermoplastic resins, derived from Southern pipe stumps and comprising a complex mixture of high molecular weight phenolic compounds and resin acids, available commercially as VINSOL resins from Hercules Powder Co. or certain Kraft lignins available commercially as INDULIN from Westvaco, Inc. Such currently available emulsifying agents are not always satisfactory in performance and are relatively expensive.
Lignosulfonates, present in spent sulfite waste liquor which results as a by-product of paper pulping operations, represent a particularly attractive source of raw material for conversion into more valuable products, particularly since waste liquor disposal is a problem for many paper manufacturers who must meet pollution standards. However, in spite of the general knowledge of certain dispersing properties of lignosulfonates, attempts to provide waste liquor lignosulfonates for use in asphalt emulsions have been largely unsuccessful. Equipment currently used in industry to produce asphalt emulsions embody any number of rotor-stator designs. The equipment design generates shearing forces that vary over a wide range, e.g., from the extremely high shearing forces of a Manton Gaulin mill to the relatively medium shearing forces of a Charlotte collid mill to the relatively lower shearing forces of a P&O machine type mill. VINSOL resins and INDULIN additives apparently are operable with such high and medium shear mills. However, attempts to produce emulsions with spent liquor lignosulfonates on such colloid mills that generate low to moderate shearing forces and that exert a slow shearing action when the components are initially admixed have not been successful, resulting in unstable emulsions containing large particles of the order of 50 microns or so. Such large particles have a grainy appearance and render the emulsions unstable upon storage, the large particles settling out of the emulsion after a short period of time. Such large particles additionally render the emulsions too unstable to be useful in many of the desirable applications, for example, as slurry seals. Thus spent liquor lignosulfonates, although abundantly and economically available, have not been commercially utilized in this area.
It is an object of this invention to provide lignosulfonate based emulsion-conditioner compositions for use in asphalt emulsions.
It is another object of this invention to provide asphalt emulsions comprising lignosulfonates derived from waste sulfite liquor which may be produced over the wide range of shearing forces generated by asphalt emulsion equipment employed in the industry.
These and other objects of the invention will be apparent from the description of the invention which follows.